Advances in diagnostics and molecular typing of Mycoplasma synoviae

Abstract

The increased clinical and economic relevance of M. synoviae a poultry pathogen causing arthritis and eggshell apex abnormalities and egg production drops prompted the Dutch poultry industry to launch a mandatory control and eradication programme for this mycoplasma species in 2013 This programme is based on monitoring of commercial poultry aiming at detection of infected flocks improving awareness, and the implementation of control measures to prevent vertical and horizontal transmission. The success of a disease control and eradication programme depends on the accurate and early detection of infected flocks. This is achieved by the regular monitoring of flocks, using adequate diagnostic tests. A qPCR for the detection of M. synoviae in case of infectious synovitis in poultry was developed and may as such contribute to the reduction of economic damage due to this disease. Adequate diagnostics become especially relevant when intervention strategies such as live M. synoviae vaccination are introduced as they jeopardize seromonitoring due to the induction of vaccinal antibodies. To overcome these problems development of a DIVA (differentiation of infected from vaccinated animals) PCR is beneficial. Test parameters of the differentiating M. synoviae qPCR were excellent, while field validation yielded good results also. Horizontal spread of the MS-H live vaccine strain from vaccinated to non-vaccinated birds located at different houses on the same farm was demonstrated. The test is recommended for assessing freedom from field M. synoviae in MS-H vaccinated flocks, but can also be used to determine shedding of MS-H. Using this PCR it was shown that vaccination with MS-H significantly reduced the shedding and horizontal spread of a M. synoviae challenge strain. Based on this findings this vaccine could be used in successive rearing flocks to populate M. synoviae infected multiple age layer farms. Although elimination of infected flocks can be a very effective disease control strategy in case of low prevalence, this is not attainable in poultry categories with high prevalence. In such cases antibiotic treatment and vaccination may be used to diminish the impact of clinical signs. Drawbacks of antibiotic treatment are the occurrence of resistance, residues and birds remain infected despite treatment. Furthermore, vaccination may help to prevent or reduce clinical signs it does not protect against infection with field M. synoviae. One of the main pillars in a control and eradication programme is the implementation of effective biosecurity measures to separate M. synoviae free flocks from those infected. The identification of risk factors for infection and subsequent adjustment of named programmes, is crucial. This can be achieved by tracing M. synoviae infections, for which reproducible molecular typing techniques are necessary. The shortcomings of M. synoviae vlhA typing prompted the development and evaluation of a Multilocus Sequence Typing (MLST) for molecular typing of M. synoviae. MLST allows both, local and global phylogenetic analysis as well as source investigation of outbreaks. Tracing of M. synoviae to unravel high risks for M. synoviae outbreaks are strongly advised if the efficiency of biosecurity programmes, which are of utmost importance in disease control, is to be maximized.